Modulated pure fluid oscillator

ABSTRACT

A modulated pure fluid oscillator wherein the amplitude of a cyclically deflected power stream is periodically modulated at a frequency which is substantially lower than the cyclical deflection frequency. Amplitude modulation is achieved by issuing a periodic modulation stream in interacting relation with the power stream at sufficient pressure to limit but not override the primary cyclical power stream deflections. The modulation stream is generated by feeding back portions of the power stream which are scooped into a cylindrical vent passage disposed adjacent an output passage of the oscillator, the vent passage pressure varying as a function of the power stream deflection amplitude. Fluid is exhausted from the vent passage which acts as a vortex valve in throttling exhaust fluid as a function of vent passage pressure. Flow not exhausted from the vent passage is recirculated to interact with and limit the deflection amplitude of the power stream. Limiting the deflection amplitude reduces flow into the vent passage to cause reduced pressure therein, thereby reducing the vortex valve throttling action and reducing the flow of recirculated fluid interacting with the power stream. Consequently, the amplitude of power stream deflections increases and the modulation cycle starts over again. The modulation frequency, being dependent on vent passage pressure can be varied either by varying the power stream pressure of controlling the fluid exhaust from the vortex valve.

United States Patent [72] Inventor Vincent F. Neradka PrimaryExaminer-Samuel Scott Rockville, Md. AttorneyHurvitz, Rose & Greene [21Appl. No. 724,473 [22] Filed Apr. 26, 1968 [45] Patented Jan. 26, 1971ABSTRACT: A modulated pure fluid oscillator wherein the 3 AssigneeBowles E i i Corporation amplitude of a cyclically deflected powerstream is periodisilv S rin ,Md cally modulated at a frequency which issubstantially lower a corporation of Maryland than the cyclicaldeflection frequency. Amplitude modulation is achieved by issuing aperiodic modulation stream in interacting relation with the power streamat sufficient pressure to limit but not override the primary cyclicalpower stream deflections. The modulation stream is generated by feeding[54] MODULATED PURE FLUID OSCILLATOR back portions of the power streamwhich are scooped into a 13 Claims 3 Drawing Figs cylindrical ventpassage disposed ad acent an output passage of the oscillator, the ventpassage pressure varying as a func- U.S. r i {ion of the ower treamdeflection amp]i[ude is ex 1 Cl 1/08 hausted from the vent passage whichacts as a vortex valve in [50] Field of Search 137/81.5 h li h t fluidas a function of vent passage pressure. Flow not exhausted from the ventpassage is recirculated to in- [56] References Cited teract with andlimit the deflection amplitude of the power UNITED STATES PATENTSstream. Limiting the deflection amplitude reduces flow into 3,158,16611/1964 Warren 137/8l.5 the vent passage to cause reduced pressuretherein, thereby 3,159,168 12/1964 Reader 137/81.5 reducing the vortexvalve throttling action and reducing the 3,185,166 5/1965 Horton et al.l37/8l.5 flow of recirculated fluid interacting with the power stream.3,228,410 1/1966 Warren et al. 137/8l.5 Consequently, the amplitude ofpower stream deflections in- 3,273,377 9/ l 966 Testerman et al.137/81.5X creases and the modulation cycle starts over again. The modu-3,379,204 4/1968 Kelley et a1. 137/81.5 lation frequency, beingdependent on vent passage pressure 3,398,758 8/1968 Unfried 137/81.5 canbe varied either by varying the power stream pressure of 3,434,4873/1969 Bauer 137/81.5 controlling the fluid exhaust from the vortexvalve.

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MODULATED PURE FLUID OSCILLATOR BACKGROUND OF THE INVENTION The presentinvention relates to pure fluid oscillators and more particularly tomodulation techniques for producing very low frequency oscillatory fluidsignals.

Prior art techniques for generating low frequency fluid signals, forexample on the order of ll()Hz., generally require pure fluidoscillators of relatively large size. for example, in negative feedbackfluidic oscillators, between negative feedback loops extend between theoutput passages of the am plifier and its control nozzles. Theoscillator output frequency is determined by the transit time requiredfor the power stream fluid to travel from the point of contact with acontrol stream, through an output passage, around the feedback loops,and back through the control nozzle to the point of contact. If very lowfrequencies are desired, concomitant long transit times must beprovided. Long transit times may be achieved by operating the oscillatorat low power stream pressure, in the case of pressure controlledoscillators, or providing relatively long feedback paths for thefeedback fluid to travel. Neither alternative is desirable for lowfrequency operation. Specifically, operation at low power streampressures results in low pressure output signals and also has thedisadvantage or providing a sporadically operative device since thefeedback fluid, having a low pressure to begin with, when subjected tothe losses inherent in the system produces a control signal having apressure which is often insufficient to cause switching of the powerstream. Where the power stream pressure is maintained sufficient toproduce power stream switching, but the length of the feedback passageis increased sufficiently to obtain the desired low frequency signal,limitations an important consideration and often preclude practicalutilization of the device.

It is therefore an object of the present invention to provide a reliablepure fluid oscillator for generating low frequency fluid signals whereinthe oscillator can be kept relatively small regardless of the outputfrequency.

It is another object of the present invention to utilize modulationtechniques in order to provide a low frequency fluidic oscillator whichis smaller than prior art oscillators having corresponding outputfrequencies.

This invention is also concerned with techniques for effectingmodulation. More specifically, there has been a relatively recentrecognition by those working in fluidics of the fact thatalternating-flow systems are more advantageous for many applicationsthan direct-flow systems. The terms altemating" and direct as applied toflow herein are analogous to the terms alternating-current (AC) anddirect-current (DC) employed in electronic systems. For example,direct-flow fluidic systems are susceptible to drift, and moreparticularly to selfgenerated noise within the fluidic components. If,instead of using the direct-flow output level of an amplifier as aninformation signal, the amplitude of an alternating flow level is soemployed, the amplifier may provide gain without being sensitive todrift. In addition, employing tuning techniques to modify the frequencyresponses of an amplifier results in higher gain in a limited frequencyband than is generally achievable in direct-flow amplifiers. Increasedutilization of alternatingflow systems has resulted in a requirement forsimple and efficient modulation techniques for fluid systems.Specifically, since it is the modulating signal which carries theinformation of interest, techniques for accurately and efficientlymodulating an alternating flow carrier become quite important.

It is therefore another object of the present invention to provide asimple technique for modulating the amplitude of an alternating flowcarrier signal in a pure fluid amplifier.

SUMMARY OF THE INVENTION In one aspect of the present invention a purefluid oscillator having a cyclically deflected power stream is amplitudemodulated by means of a modulation control stream which periodicallyvaries the deflection amplitude of the power stream at a frequency whichis substantially lower than the power stream cyclical deflectionfrequency. The modulation control stream is derived from power streamfluid received by a vent passage disposed adjacent an output passage ofthe oscillator so as to scoop a portion of the power stream into thevent passage. Fluid exhaust from the vent passage is controlled by avortex valve disposed at the downstream end of the vent passage. Exhaustof fluid via the vent passage is throttled by the valve, the exhaustbeing increasingly throttled as the fluid flow received by the ventpassage increases. A recirculation path is provided 1 from the valve toa location adjacent the upstream portion of the cyclically deflectedpower stream-For large amplitudes of deflection of the oscillating powerstream relatively large portions of the power streams are received'bythe vent passage. This in turn heavily throttles the valve andrelatively large proportions of the fluid received by the vent passageare recirculated to interact with the power stream. C onsequently, theamplitude of deflection of the power stream is limited, thereby limitingthe amplitude of the output signal and also reducing the amount of fluidreceived by the vent passage. The reduction in fluid received by thevent passage reduces throttling at the vortex valve, thereby reducingrecirculated modulation flow. The limiting effect on the amplitude ofdeflection of the power stream is thereby removed, whereupon the powerstream deflection amplitude increases fluid directed to the ventpassage. Increased fluid flow to the vent passage begins the modulationcycle once again. It will be seen therefore that the amplitude ofdeflection of the power stream is cyclically limited by cyclicallyincreasing recirculation flow. The resulting output signal takes theform of an amplitude modulated wave which may be detected and filteredas to provide an oscillatory fluid signal having a frequency determinedby the throttling action of the vortex valve, the length of therecirculation path, and the power stream pressure.

Since exhaust flow is proportional to the pressure in the vent passage,it follows that increasing power stream pressure serves to increasethrottling at the vortex valve so as to increase the buildup ofrecirculated modulation and control flow and thereby increase thefrequency of the modulation signal. If the modulated output signal fromthe oscillator is filtered by a low pass filter so as to block thecarrier or deflection frequency of the oscillator, only the modulationfrequency will be recovered, and this frequency can be controlled as afunction of the power stream pressure. Thus a low frequency oscillatorcan be provided without requiring excessively large fluidic devices.Further, control of the modulation frequency may be achieved other thanby varying the power stream pressure. Specifically, the throttlingaction of the vortex valve may be varied as a function of variation insize of the output port in the vortex valve. Similarly, introduction ofadditional fluid flow into the exhaust port of the vortex valve caneffect valve throttling as desired and thereby vary the frequency of themodulating signal.

It is important to bear in mind that the length of the path traveled bythe recirculating control fluid, namely the vent passage length added topath length within the vortex valve and the recirculation pathcommunicating with the power stream, determines in part the modulationfrequency. Naturally, changes in power stream pressure and externallycontrolled valve throttling will produce variations of this frequency asdetermined by the circulation path; however, it is the transmission timeof the vented flow around this recirculation path which is the primarydetermining factor. Since the recirculation path receives only theboundary portions from the power stream, which are at substantiallylower pressures than the power stream core, the recirculation time forthe modulation signal is substantially longer than the recirculationtime for the main portion of the power stream around a path of a similarlength In addition, the recirculation time for the modulation signal isextended relative to the recirculation time for the main portion of thepower stream due to the frequency response of the vortex valve action inthe vent passages.

In a second embodiment of the invention a fluidic beat frequencyoscillator is obtained by mixing two oscillating fluid signals ofslightly different frequencies. The mixed signals are then detected andpassed through a low pass filter to provide the desired beat frequencyoutput. If one of the mixed signals is generated by a fixed frequencyoscillator, and the other signal is generated by a pressure controloscillator. the beat signal frequency is variable as a function of theinput pressure to the pressure controlled oscillator.

BRIEF DESCRIPTION OF THE DRAWINGS The above and still further objects,features and advantages of the present invention will become apparentupon consideration of the following detailed description of severalspecific embodiments thereof, especially when taken in con junction withthe accompanying drawings, wherein:

FIG. I is a plan view of a self-modulating pure fluid oscillatorconstructed in accordance with the principles of the present invention;

FIG. la is an illustrative waveform representing a typical signal at theoutput passages of the device of FIG. l; and

FIG. 2 is a schematic representation of another embodiment of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now specifically toFIG. 1 of the accompanying drawings, there is illustrated a negativefeedback pressure controlled oscillator employing the principles of thepresent invention. It is to be understood that applicability of theprinciples of the present invention is not limited to negative feedbacktype oscillators, but rather are appropriate in any pure fluid devicehaving an oscillatory power stream. The oscillator of FIG. I issubstantially similar to the oscillator described in copending US. Pat.application Ser. No. 430,696 by F. Manion, filed Feb. 5, 1965, nowabandoned and assigned to the same assignee as the present invention,and comprises a pure fluid proportional amplifier generally designatedby the reference numeral 1. The cavities, passages, and nozzles neededto provide the pure fluid amplifier I are formed in a flat plate It andplate it is covered by a flat plate 12, the two plates being sealed influid tight relationship, one to the other, by means of machine screws,clamps, adhesives, or the like. For the purposes of clarity, the platesill and 12 are shown to be composed of a clear plastic material,however, it should be understood that any material compatible with theworking fluid may be used in the construction of the amplifier.Amplifier 1 has a power nozzle 2, control nozzles 3 and 4, and a pair ofoutput passages 6 and 7 located downstream of the nozzles. The sidewallsof the amplifier are removed by providing recesses 8 and 9 which arevented to ambient pressure via exhaust port 16 and 17 respectively toprevent boundary layer effects from affecting the position of the powerstream. Output passages 6 and 7 are separated from respective recesses 8and 9 by means of flow dividers I3 and 14, respectively. Exhaust portsor apertures 16 and I7 are defined through cover plate I2 so as tocommunicate between the downstream ends of respective recesses 8 and 9and ambient pressure via respective exhaust tubes 3! and 32.

In the embodiment of FIG. ll, a pair of RLC feedback loops are provided,extending respectively from output passage 6 to control nozzle 3 andoutput passage 7 to control nozzle 4. More particularly, the feedbackloop extending from output passage 6 comprises inductance (inertance)119 which constitutes a relatively long narrow passage, a capacitor 2icomprising an enlarged volume in series with inductance 19, and afurther inductance 22 having a restriction 23 in series therewith torepresent the resistance of the feedback path. Restrictor 23 need notexist as such a in a high 7 system, the necessary resistance beingpresent in the amplifier per se. In a highly damped system, on the otherhand, a restrictor such as 23 or a porous plug or other type of fluidresistance may be employed. A similar feedback path comprising similarcomponents exists between output passage 7 and control nozzle 4. Thisfeedback path is substantially identical with the feedback pathpreviously described in order to provide symmetrical oscillatoryoperation and therefore will not be described in further detail. It isto be understood however that if asymmetrical oscillationis desired, thetwo feedback paths may include either different components or similarcom ponents having different parameter values.

Upon issuance ofa power stream from the nozzle 2, a larger proportion ofthe stream flows to one or the other of the output passages o-or 7 dueto some initial perturbation of the stream. Assuming for the moment thata greater proportion of the flow is to the passage 6, fluid is fed backthrough the feed' back loop extending therefrom and issues from controlnozzle 3 so as to divert the power stream to output passage 7. Fluidsupplied to output passage 7 then proceeds around the feedback loopextending therefrom and upon issuing from nozzle 4 diverts the powerstream back to output passage 6. Thus the power stream oscillates backand forth between passages 6 and 7 at some frequency which is equal tothe total transport time of the fluid about the system. The transporttime is determined by the lengths of the output passages, and thefeedback paths as well as the values of the RLC components in thefeedback pathsl It is readily apparent that the frequency of oscillationis also a function of the pressure of the power stream, since the totaltransport time of the fluid about the feedback loops reduces as thepressure increases, thus tending to increase the frequency ofoscillation with increase in pressure.

The system as thus far described is substantially identical with thepressure control oscillator described in the abovereferenced copendingpatent application Se'r. No. 430,696 except that the pressure-controlledoscillator of said patent application provides conventional relativelylarge vent ports at the downstream ends of recesses 8 and 9 so as tomaintain these recesses at I ambient pressure throughout the entireoperating range of the oscillator. In the present invention, however,relatively small exhaust ports 16 and 17 are provided and serve as asink for exhausting fluid from the recesses 8 and 9, respectively. Thedownstream ends of passages 8 and 9 are curved to induce rotational orvertical flow in fluid received' by the recesses 8 and 9 by virtue ofdeflection of the power stream at least partially beyond the apices offlow dividers l3 and I4. Fluid received by recess 8, for example, isdirected around the periphery of the recess into a vortical path and isexhausted through aperture 16. The relatively small diameter of exhaustaperture 16 gives rise to a high velocity circulation at the core of thevortex which in turn gives rise to a throttling effect on the exhaustingflow. The throttling action increases with increasing vortical flow, andvortical flow increases with increased power stream flow into recess 8.It is apparent that the greater the amplitude of oscillations of thepower streams, the greater the flow into the recess 8. As the throttlingaction increases more of the power stream spillage received by therecess is spun around the periphery of the recess by the centrifugalforce created at'the periphery of the vortex. This por' tion of thespillage cannot be exhausted due to the increased throttling and istherefore fed back along the recess wall into interacting relationshipwith the power stream at a location slightly downstream thecontrol'nozzle 3. The greater the spillage received by recess 8 thegreater the flow returned to interact with the power stream. Therecirculated spillage serves two separate functions: first, it increasesthe pressure in the power stream; second, it provides a secondarycontrol stream. This secondary controlstream acts to limit deflection ofthe power stream towards recess 8 and thereby reduce the amplitude ofoscillation of the power stream. The resulting smaller swing oramplitude of the power stream results in less spillage into recess 8 andconsequently in less secondary con trol stream flow interacting with thepower stream. Consequently the amplitude of the power stream beginsincreasing and spillage flow into recess 8 increases, thereby increasingthe vorticity of the exhaust flow in the recess which in turn producesan increased throttling action of the exhaust flow. As

discussed above, increased throttling causes a return of more of thespillage fluid into interacting relationship with the power stream aspart of the secondary control stream.

It is seen that the effects of the secondary control stream on theamplitude of the oscillating power stream are cyclical, occurring at afrequency determined by the pressure of the fluid received by recess 8,the strength of the vortex created about exhaust port 16, and the lengthof the peripheral path defining the boundary walls of the recess for anygiven size of port 16. The secondary control stream thus serves toamplitude-modulate the oscillator output signal provided at outputpassage 6 of the oscillator. In a similar manner, a secondary controlstream is provided about the periphery of recess 9 by means of thevortical flow induced about exhaust aperture 17. In a unit which isentirely symmetrical about the longitudinal axis of power nozzle 2, thetwo secondary control streams are in phase so that a cyclicalcompressive force is applied at both sides of the power stream to limitthe amplitude or swing of the power stream in both directionssimultaneously, This factor has been borne out by data resulting fromtests of the device illustrated in FIG. 1. This in-phase bcating" by thesecondary control streams is contrary to the 180 out-of-phaserelationship existing between the control signals employed at controlnozzles 3 and 4 to cyclically deflect the power stream at theoscillation or carrier frequency. As a result, the output signalsappearing across output passages 6 and 7 is an amplitude modulatedsignal in which the carrier frequency is determined by the transmit timefor fluid traversing the output passages, feedback paths, and thecontrol nozzles, whereas the modulation frequency is determined by thefluid transit time about the periphery of recesses 8 and 9. The outputwaveform, appearing as a differential pressure across passages 6 and 7,is illustrated in FIG. 1a.

Even though the actual path length about the recesses 8 and 9 issubstantially shorter than the feedback path length from output tocontrol passages, the modulation frequency is substantially lower thanthe basic oscillator carrier frequency. The reason for this is two fold:first of all the power stream has a bell-shaped transverse pressuregradient so that the spillage portion of the power stream received bythe vent passages is at a substantially lower pressure and velocity thanthe core of the power stream which is received by output passages 6 and7. A secondary factor accounting for the substantially lower frequencyof the secondary control signal as compared with the feedback signal isthe time required to increase and decrease the vorticity of flow in thevent passages.

The throttling action of the vortexes created in the vent passages maybe likened to the action of a vortex valve such as the type disclosed inUS. Pat. No. 3,324,891 to Rhoades. Specifically, in a vortex, therotating fluid creates a centrifugal force so that there is a relativelylarge pressure at the outside of the vortex and a pressure gradientacross the vortex. The centrifugal force is a function of the vorticalvelocity of the fluid which in turn is a function of the fluid flow inrecesses 8 and 9 in the unit of FIG. 1. Thus as the flow into a recessincreases the centrifugal force created by the vortex increases, therebyincreasingly throttling exhaust from the recess and increasing the flowreturned to interact with the power stream.

Since the modulation frequency is dependent to an extent on the pressureof the fluid received by the recesses 8 and 9, it is not surprising thatthe modulation frequency can be varied (along with the carrierfrequency) as the power stream pressure is varied. Tests have shown thatfor a unit configured substantially like that illustrated in FIG. 1, alinear modulation frequency versus power stream pressure characteristicis achievable by varying the power stream pressure over a predeterminedrange. This provides a self-controlled feature whereby the modulationfrequency can be adjustably set to a desired value. This is particularlyadvantageous where it is desired to utilize the modulation frequency asa low frequency oscillatory signal. Specifically, output passages 6 and7 may be connected to a rectifier 26 such as the full wave rectifierdisclosed in US. Pat. No. 3,292,648 To .l. R. Colston. The full waverectified signal may then be passed to a low pass filter 27 which blocksall carrier signal components and passes a signal at twice themodulation frequency the modulation frequency being doubled by virtue offull wave rectification. The output of the low pass filter 27 therebyconstitutes a low frequency oscillatory signal, the frequency of whichmay be readily controlled, such as by controlling the pressure of thepower stream issued from nozzle 2. Low pass filter 27 may, for example,be of the type described in the above-referenced Colston patent. Insteadof using rectifier 26 and filter 27 to obtain the low frequencyoscillatory signal, I have found that a turbulence amplifier, such asthe type disclosed in copending US. Pat. No. 3,234,955, may serve thesame purpose. Specifically, if each of output passages 6 and 7 isconnected to a power stream tube of respective turbulence amplifiers,the output passagesof the turbulence amplifiers receive the lowfrequency modulation fluid signal without any carrier signal component.The reason for this is the relatively high inductance of the powerstream tubes of the turbulence amplifiers, such inductance rendering theturbulence amplifier incapable of responding to the relatively highcarrier frequency signal. It is important, of course, that a turbulenceamplifier having a sufficiently high inductance be chosen for thispurpose.

As discussed previously, the large components required to produce lowfrequency oscillations in prior art pure fluid devices are extremelydisadvantageous and uneconomical. The modulation technique employedherein to produce low frequency oscillations with the use of rectifier26 and low pass filter 27 avoids the disadvantages inherent in the priorart. In addition, both the carrier and modulation frequencies aregenerated with a single fluid amplifier element, thereby avoiding theuneconomical and inefficient prior art fluidic modulation techniquesrequiring separate fluid amplifier elements to generate the carrier andmodulation signals.

It is to be noted that the frequency versus pressure characteristics ofboth the carrier and modulation signals are such to enable frequencymodulation of both signals by varying the power stream pressure. Thus,where a sinusoidal pressure is applied at power nozzle 2 both themodulation signal and the carrier signal are frequency modulated at thesinusoidal signal frequency and can be appropriately employed forseparate or concurrent utilization. Thus, the device of the presentinvention is suitable for both amplitude and frequency modulationtechniques.

The amplitude modulation feature of the present invention can be used toeven further advantage than previously described. Specifically, thethrottling action of the vortex valve in vent passages 8 and 9 may beenhanced or retarded in various ways to effect variations in amplitudeand frequency of the recirculated secondary control stream. Thus,control signals may be tangentially applied at the periphery of the ventrecesses 8 and 9 in either aiding or impeding relation to the peripheralspillage flow received by the recess. Moreover, the effective size ofexhaust apertures 16 and 17 may be adjusted as desired in accordancewith input information, or the apertures l6 and 17 may be blocked bysome external member such as a piston moving axially of the aperture ora plate moving perpendicularly thereof so as to vary the throttlingaction of the vortex in these recesses as a function of some desiredinput information signal. Valves connected in series with pipes 31 and32 may accomplish this function. The input information signal may thenbe recovered by demodulating the output signal appearing at outputpassages 6 and 7 by utilizing a nonlinear element such as a rectifier 26connected thereacross.

ln tests performed on an oscillator configured substantially asillustrated in FIG. 1, it was found that the modulation frequency variedlinearly from 5 to l0 Hz. in response to input pressure variationbetween 0.053 to 0.060 p.s.i.g. For the same input pressure variation,the carrier frequency was found to vary linearly between approximatelyI40 and Hz. In the units tested, the limits of the modulation frequencyrange were approximately 2 Hz. and I1 Hz. For input pressures outsidethe range for producing these modulating frequencies, the

units operated as simple sine wave oscillators, producing only thecarrier frequency signal.

An interesting phenomenon was observed during testing, namely thesensitivity of the above-described unit to externally generated noise.For example, a unit operating at or near an end of its modulation rangewas found to switch to pure carrier mode of operation (withoutmodulation) in response to the snap of ones fingers in the vicinity ofthe unit. This phenomenon would appear to render the unit of FIG. 1suitable for operation as an acoustic detector, providing a lowfrequency signal from filter 27 unless disturbed by an acoustic signalabove a predetermined amplitude and within a specified frequency range.

In addition to the acoustic sensitivity of the modulation signal in thedevice of FIG. 1, it has been found that the carrier frequency is alsosensitive to externally provided acoustic signals. Specifically,operating the PCO outside the modulation range, it was found that thePCO frequency changed when subjected to acoustic signals at certainfrequencies, but remained constant when subjected to signals throughoutthe remainder of the audio frequency range. Depending upon the operatingfrequency of the PCO, the number of audio frequencies to which the PCOwas sensitive changed. For example, only one audio frequency was foundto change the frequency of the PCO originally set to operate at 102l-lz.;

however, when the PCO was originally set to operate at 104 l-Iz., twodistinct audio frequencies produced PCO frequency changes. Further, whensubjected to an audio frequency to which it is frequency-sensitive, thePCO frequency variation was found to vary as a function of the audiosignal level at that sensitive frequency.

In view of the above, it would appear that the FCC illustrated in FIG.1, apart from its self-modulating capability, is capable of beingmodulated by acoustic signals at predetermined frequencies and by anamount determined by the acoustic signal level at these predeterminedfrequencies. The FCC could therefore serve as sonic detector; or wherean acoustic signal generator is provided in proximity to the FCC, theFCC may be selectively modulated in accordance with input informationcontrolling the actuation of the acoustic signal generator.

Referring now to FIG. 2 of the accompanying drawings, there isillustrated in schematic form another embodiment of the presentinvention wherein modulation techniques are employed to provide lowfrequency oscillatory fluid signals. More specifically, a pair ofpressure controlled oscillators and 60 are provided and by way ofexample may be of the type described in the above-referenced copendingPat. application Ser. No. 430,696 by F. M. Manion. Oscillator 40receives an input pressure signal P at its power nozzle 41 andoscillator 60 receives an input pressure signal P at its power nozzle6i. Oscillatory differential pressures are provided across outputpassages 43 and 45 of oscillator 40 and 63 and 65 of oscillator 60 asfunctions of respective input pressure signals P and P Output passages43 and 45 are connected to opposing control nozzles i and 53respectively of a proportional fluidic amplifier 50. Output passages 63and 65 are connected to opposing control nozzles 71 and 73 respectivelyof a proportional fluidic amplifier 70. Amplifiers 50 and 70, by way ofexample, may be of the type described and illustrated in U.S. Pat. No.3,275,013. Amplifiers 50 and 70 are provided with respective pairs ofoutput passages 55, 57 and 75, 77. Output passages 55 and 75 areconnected together at a common point by means of a T-fitting 8i;similarly output passages 57 and 77 are connected to a common point bymeans of T-fitting 83. T-fittings 81 and 83 are not to be construed aslimiting but rather as illustrative of one of the numerous conventionaltechniques by which two fluidic signals may be connected to a commonpoint. The output signals from the T-fitting 81 is applied as an inputsignal to a rectifier 85, the output signal from which is applied to alow pass filter 87. Similarly, the signal from fitting 83 is applied torectifier 86 and low pass filter 88. Rectifiers 85, 86 and filters 87,88 may, for example, be identical to rectifier 26 and filter 27 of FIG.1.

In operation, assume that the frequencies of the output signals fromoscillators $0 and 60 are slightly different. This may be achieved byemploying identical oscillators and providing input signals P, and P atslightly different pressures; or the oscillators themselves may beconstructed to operate at different frequencies for equal inputpressures. The slightly different frequency signals are fed torespective buffer amplifiers 50 and 70 which serve to isolate the twooscillators from one another and thereby prevent mutual feedback betweenoscillators to produce frequency distortion. The beat frequency (ordifference frequency) between the two amplifier output signalfrequencies is generated at fittings 81 and 83 with a l-phasedifference, and recovered by respective rectifiers 85, 36 and filters87, 38, the latter passing only low frequency signals and blockingfrequencies on the order of the PCO output frequencies. A low frequencysignal may thus be obtained by spacing the frequencies of PCOs 40 and 60as desired.

It is to be understood that the differential ,or push-pull configurationillustrated and described above is by way of example only. If desired,the individual output signals from fittings 81 and 83 may be used alone,rectified and filtered to provide a single-ended device wherein a lowfrequency output signal is provided.

If input signal P, is held at constant pressure and input signal I ismade'variable in response to a predetermined parameter, the modulationsignal appearing at the output passage of low pass filter 87 is aprescribed function of the predetermined parameter. If PCO 60 has alinear frequency versus pressure characteristic, said prescribedfunction is linear and represents a gain (in cycles per second versuspsi.) which is almost twice the gain of FCC 60' alone. Similarly, whereP and P, are made to vary differentially in response to thepredetermined parameter, even higher gains, on the order of four timesthat of a single PCO, are achievable.

In a circuit configured substantially as that of FIG. 2, it was foundthat a frequency range from substantially 0 to 25 Hz. was obtainable,and that the frequency was linear with respect to input pressurevariations over the range from 0.5 to 20 Hz.

The utilization of pressure controlled oscillators 40 and 60 in theembodiment of FIG. 2 should not be considered as limiting the scope ofthe present invention. Specifically, any two fluidic oscillators havingtheir frequencies separated as desired would suffice to provide therequisite low frequency signal at filters 37 or 88. The advantage ofpressure controlled oscillators resides primarily where P and P arevariable relative to one another and the low frequency output signal isa function of the input pressure variation.

While I have described and illustrated several specific embodiments ofmy invention, it will be clear that variation of the details ofconstruction which are specifically illustrated and described may beresorted to without departing from the spirit and scope of the inventionas defined in the appended claims.

I claim:

1. A fluidic element comprising:

nozzle means responsive to application of pressurized fluid thereto forissuing a power stream of fluid; oscillatory control means forcyclically transversly deflecting said power stream at a carrierfrequency;

output means for selectively receiving the deflected power stream; and rmodulating means for cyclically limiting the deflection amplitude ofsaid power stream at a modulation frequency which is substantially lowerthan said carrier frequency; said modulating means comprising: a ventpassage in said element disposed for receiving varying power stream flowin proportion to the deflection amplitude of said power stream; exhaustport means disposed near the downstream end of said vent passage andcommunicating with an ambient pressure environment, said exhaust portmeans being configured wherein its maximum fluid exhaust flow rate issmaller than the power stream flow rate into said vent passage formaximum deflection amplitude of said power stream; and recirculationmeans responsive to power stream flow rates into said vent passage inexcess of said maximum fluid exhaust flow rate for directing a fluidmodulating stream into interacting relation with said power stream, saidmodulating stream having a maximum momentum which is sufficient to limitthe deflection amplitude of said power stream and insufficient toentirely override said oscillatory control means.

2. The combination according to claim 1 wherein the downstream end ofsaid vent passage is curved sufficiently to induce vortical flow aboutsaid exhaust port means in response to fluid flow in said vent passage,saidvortical flow throttling fluid exhaust from said exhaust port as afunction of the power stream flow into said vent passage, and whereinsaid recirculation means includes a sidewall of said vent passagedisposed for receiving peripheral fluid from said vortical flow as afunction of vortical flow rate and for directing said peripheral fluidinto interacting relation with said power stream.

3. The combination according to claim 1 further comprising demodulationand low pass filter means connected to said output passage for providinga fluid output signal at said modulation frequency and for blocking saidcarrier frequency.

4. A fluidic element comprising: nozzle means responsive to applicationof pressurized fluid thereto for issuing a power stream of fluid,oscillatory control means for cyclically transversely deflecting saidpower stream at a carrier frequency; output means for selectivelyreceiving the deflected power stream; said output means comprising apair of output passages disposed for selectively receiving said powerstream; modulating means for cyclically limiting the deflectionamplitude of said power stream at a modulation frequency which issubstantially lower than said carrier frequency; said modulating meanscomprising: a pair of vent passages, each disposed adjacent a respectiveoutput passage and separated therefrom by respective flow dividers, saidvent passages being disposed to receive power stream fluid only inresponse to transverse deflections of said power stream beyond saidrespective output passages, each said vent passages having an exhaustport communicating between its downstream end and ambient pressure, thewalls of each vent passage being curved to produce vortical flow aboutsaid exhaust port in response to power stream flow into said ventpassage, said vortical flow throttling fluid exhaust via said exhaustport as a function of the flow rate into said vent passage, said exhaustport being sufficiently small and said vent passage wall being soconfigured that for large power stream deflections by said oscillatorycontrol means a substantial portion of the fluid received by said ventpassage is circulated about the periphery of the vortical flow and backinto interacting relation with said power stream, the maximum momentumof the flow so circulated being sufficient to reduce but not overridethe deflection amplitude of said power stream produced by saidoscillatory control means.

5 The combination according to claim 4 further comprising demodulationand low pass filter means connected to said output passages forproviding a fluid output signal at said modulation frequency and forblocking said carrier frequency.

6. The combination according to claim 4 where said ele ment is apressure controlled oscillator in which said modula tion frequency andsaid carrier frequency vary as functions of the pressure of the fluidapplied to said nozzle meansv 7. The combination according to claim 6where said oscillatory control means includes negative feedback passagesextending from each of said output passages for applying a por tion ofthe flow received by each output passage in interacting relation withsaid power stream.

8. The combination according to claim 7 further comprising demodulationand low pass filter means connected to said output passages forproviding a fluid output signal at said modulation frequency and forblocking said carrier frequency.

9. The method of monitoring an acoustic disturbance utilizing a pressurecontrolled fluidic oscillator in which a power stream of fluid iscyclically transversely deflected and which has a variable power streamdeflection frequency versus input pressurecharacteristic, said methodcomprising the steps of:

ad usting the frequency of said pressure controlled oscillator to avalue from which a predetermined power stream deflection frequencydeviation ensues in response to said acoustic disturbance;

subjecting said pressure controlled oscillator to said acousticdisturbance; and

monitoring the power stream deflection frequency of said pressurecontrolled oscillator to provide an indication in response to saidpredetermined power stream deflection frequency deviation.

10. The method of generating a low frequency fluid signal comprising thesteps of:

issuing a power stream of fluid at a specified pressure;

cyclically deflecting said power stream transversely of its flowdirection and at a predetermined amplitude and frequency of deflection;

cyclically limiting the amplitude of deflection of said power stream ata lower frequency than said predetermined frequency by recirculating atleast one low velocity portion of said power stream into deflectingrelationship with said power stream, the portion of said power stream sorecirculated being dependent upon the amplitude of deflection of saidpower stream such that more fluid is recirculated for high deflectionamplitudes than low deflection amplitudes.

11. The method according to claim 10 wherein said step of cyclicallylimiting includes the step of recirculating fringe portions of saidpower stream into deflecting relationship with said power stream, theamount of fluid so recirculated being relatively large when thedeflection amplitude of said power stream is maximum and relativelysmall when the deflection amplitude of said power stream is minimum.

12. The method according to claim 11, wherein said predeterminedfrequency is a function of said specified pressure and wherein saidspecified pressure is selectively variable.

13. The method according to claim 11 further comprising the step ofselectively impeding and augmenting the recirculating fluid to vary saidlow frequency.

1. A fluidic element comprising: Nozzle means responsive to applicationof pressurized fluid thereto for issuing a power stream of fluid;oscillatory control means for cyclically transversly deflecting saidpower stream at a carrier frequency; output means for selectivelyreceiving the deflected power stream; and modulating means forcyclically limiting the deflection amplitude of said power stream at amodulation frequency which is substantially lower than said carrierfrequency; said modulating means comprising: a vent passage in saidelement disposed for receiving varying power stream flow in proportionto the deflection amplitude of said power stream; exhaust port meansdisposed near the downstream end of said vent passage and communicatingwith an ambient pressure environment, said exhaust port means beingconfigured wherein its maximum fluid exhaust flow rate is smaller thanthe power stream flow rate into said vent passage for maximum deflectionamplitude of said power stream; and recirculation means responsive topower stream flow rates into said vent passage in excess of said maximumfluid exhaust flow rate for directing a fluid modulating stream intointeracting relation with said power stream, said modulating streamhaving a maximum momentum which is sufficient to limit the deflectionamplitude of said power stream and insufficient to entirely overridesaid oscillatory control means.
 2. The combination according to claim 1wherein the downstream end of said vent passage is curved sufficientlyto induce vortical flow about said exhaust port means in response tofluid flow in said vent passage, said vortical flow throttling fluidexhaust from said exhaust port as a function of the power stream flowinto said vent passage, and wherein said recirculation means includes asidewall of said vent passage disposed for receiving peripheral fluidfrom said vortical flow as a function of vortical flow rate and fordirecting said peripheral fluid into interacting relation with saidpower stream.
 3. The combination according to claim 1 further comprisingdemodulation and low pass filter means connected to said output passagefor providing a fluid output signal at said modulation frequency and forblocking said carrier frequency.
 4. A fluidic element comprising: nozzlemeans responsive to application of pressurized fluid thereto for issuinga power stream of fluid, oscillatory control means for cyclicallytransversely deflecting said power stream at a carrier frequency; outputmeans for selectively receiving the deflected power stream; said outputmeans comprising a pair of output passages disposed for selectivelyreceiving said power stream; modulating means for cyclically limitingthe deflection amplitude of said power stream at a modulation frequencywhich is substantially lower than said carrier frequency; saidmodulating means comprising: a pair of vent passages, each disposedadjacent a respective output passage and separated therefrom byrespective flow dividers, said vent passages being disposed to receivepower stream fluid only in response to transverse deflections of saidpower stream beyond said respective output passages, each said ventpassages having an exhaust port communicating between its downstream endand ambient pressure, the walls of each vent passage being curved toproduce vortical flow about said exhaust port in response to powerstream flow into said vent passage, said vortical flow throttling fluidexhaust via said exhaust port as a function of the flow rate into saidvent passage, said exhaust port being sufficiently small and said ventpassage wall being so configured that for large power stream deflectionsby said oscillatory control means a substantial portion of the fluidreceived by said vent passage is circulated about the periphery of thevortical flow and back into interacting relation with said power stream,the maximum momentum of the flow so circulated being sufficient toreduce but not override the deflection amplitude of said power streamproduced by saiD oscillatory control means. 5 . The combinationaccording to claim 4 further comprising demodulation and low pass filtermeans connected to said output passages for providing a fluid outputsignal at said modulation frequency and for blocking said carrierfrequency.
 6. The combination according to claim 4 where said element isa pressure controlled oscillator in which said modulation frequency andsaid carrier frequency vary as functions of the pressure of the fluidapplied to said nozzle means.
 7. The combination according to claim 6where said oscillatory control means includes negative feedback passagesextending from each of said output passages for applying a portion ofthe flow received by each output passage in interacting relation withsaid power stream.
 8. The combination according to claim 7 furthercomprising demodulation and low pass filter means connected to saidoutput passages for providing a fluid output signal at said modulationfrequency and for blocking said carrier frequency.
 9. The method ofmonitoring an acoustic disturbance utilizing a pressure controlledfluidic oscillator in which a power stream of fluid is cyclicallytransversely deflected and which has a variable power stream deflectionfrequency versus input pressure characteristic, said method comprisingthe steps of: adjusting the frequency of said pressure controlledoscillator to a value from which a predetermined power stream deflectionfrequency deviation ensues in response to said acoustic disturbance;subjecting said pressure controlled oscillator to said acousticdisturbance; and monitoring the power stream deflection frequency ofsaid pressure controlled oscillator to provide an indication in responseto said predetermined power stream deflection frequency deviation. 10.The method of generating a low frequency fluid signal comprising thesteps of: issuing a power stream of fluid at a specified pressure;cyclically deflecting said power stream transversely of its flowdirection and at a predetermined amplitude and frequency of deflection;cyclically limiting the amplitude of deflection of said power stream ata lower frequency than said predetermined frequency by recirculating atleast one low velocity portion of said power stream into deflectingrelationship with said power stream, the portion of said power stream sorecirculated being dependent upon the amplitude of deflection of saidpower stream such that more fluid is recirculated for high deflectionamplitudes than low deflection amplitudes.
 11. The method according toclaim 10 wherein said step of cyclically limiting includes the step ofrecirculating fringe portions of said power stream into deflectingrelationship with said power stream, the amount of fluid so recirculatedbeing relatively large when the deflection amplitude of said powerstream is maximum and relatively small when the deflection amplitude ofsaid power stream is minimum.
 12. The method according to claim 11,wherein said predetermined frequency is a function of said specifiedpressure and wherein said specified pressure is selectively variable.13. The method according to claim 11 further comprising the step ofselectively impeding and augmenting the recirculating fluid to vary saidlow frequency.